I wonder the same thing. This seems like a solution in search of a problem. For your average blog, a spam filter plus a moderation queue for first-time posters works just fine.
Also, if a site asks me to use someone else's credentials to comment, I probably won't bother. Why should my hobby-coding account on Github, or my spam-catching account on Gmail, be linked to your blog about philately or bird-watching?
Also, if a site asks me to use someone else's credentials to comment, I probably won't bother. Why should my hobby-coding account on Github, or my spam-catching account on Gmail, be linked to your blog about philately or bird-watching?